This invention concerns a line to produce strip and/or sheet.
To be more exact, the production line according to the invention is suitable for the balancing of the various components and for optimising the yield of a production plant for the rolling in line of strip and/or sheet, starting from the continuous casting of thin or medium slabs, and also for ensuring a high level of output.
By thin slabs are meant slabs with a width of 700 to 2500 mm. and with a thickness of 30 to 60 mm., whereas by medium slabs are meant slabs with a width of 700 to 2500 mm. and with a thickness of 60 to 130 mm.
Rolling lines to produce thin and medium strip or sheet are disclosed in the state of the art; the types usually employed in the state of the art are substantially two in number.
A first type of line arranges that the continuously cast slab, after being sheared to size, is sent into a temperature-restoration furnace of a combustion type.
The slab passing through this temperature-restoration furnace at a low speed has to stay therewithin until the temperature of the material has been brought to the necessary value most suitable for the subsequent processes.
This method entails the use of furnaces of great sizes up to 150 meters or more together with problems linked to the costs of investment, the power employed for heating, maintenance of the plant and also with problems connected with an imperfect productivity of the plant.
The segment of slab at the outlet of the combustion furnace is accelerated and then sent for rolling.
A second type of plant, such as those of EP-A-0107991 or U.S. application Ser. No. 5,156,800 for instance, provides a quick-heating assembly, an induction furnace for example, located downstream of the continuous casting plant and of the shearing-to-size assembly and followed by a furnace which makes homogeneous and equal the temperature of the slab.
The slab is passed at a low speed through the induction furnace so as to limit the requirement of power and is sent thereafter to a rolling train located at the outlet of the quick-heating assembly.
The rolling train works at a low speed with problems of thermal stress of the rolling rolls.
This requires the use of a rolling train oversized as compared to the other components of the plant.
This entails also an imperfect exploitation of the working assemblies of the production line.
The present applicants have designed, tested and embodied this invention to overcome the shortcomings of the state of the art and to achieve further advantages.